I guess the title says it all. I've been successfully working with @font-face (with near-perfect cross-browser support, if you use all the hacks).
However, a client really wants to use Helvetica, and for that you need to use Montype's solution from fonts.com.
Has anyone come across a comprehensive comparison, or have first-hand experience with both approaches? Are there any downsides (other than a monthly subscription fee!!!) to the fonts.com webfont approach?